Poppet valve

ABSTRACT

Provided is a poppet valve capable of realizing maximum. combustion efficiency all of three heat transfer forms. In a poppet valve including a head portion ( 14 ) formed integrally with one end side of a stem portion ( 12 ), in the head portion ( 14 ), a hollow portion ( 19 ) extending along a head surface ( 24 ) is formed, a metal layer ( 17 ) that insulates. radiation heat is formed on a upper end surface ( 25 ) of the hollow portion ( 19 ), and a heat insulating portion is formed between the metal layer ( 17 ) and a bottom surface of the hollow portion ( 19 ). Among the heat. transfer forms, conduction and convection are insulated by the heat insulating portion, and radiation is insulated by the metal layer ( 17 ).

TECHNICAL FIELD

The present invention relates to a poppet valve that suppresses dissipation of heat caused by heat transfer, specifically, radiation from a combustion chamber.

BACKGROUND ART

Patent Literatures 1 describes poppet valves each including a head portion formed integrally with a stem end portion. A poppet valve to be used in an internal combustion drives an engine by opening and closing an intake passage or an exhaust port by being seated on a valve seat of a cylinder head to which the intake passage or the exhaust port is connected.

Normally, in an internal combustion, the smaller the energy loss in a combustion chamber, the higher the combustion efficiency. Energy loss includes cooling loss caused by scattering of heat to the outside, etc. Heat in the combustion chamber dissipates to the outside via the poppet valve and a combustion chamber inner wall in many cases. Therefore, in or near a head surface of the poppet valve which comes into contact with the combustion chamber, a space is formed, and by forming a vacuum in this space, filling with an inert gas, or filling with a material having lower heat conductivity than a material forming the poppet valve, a heat insulating space is formed to suppress dissipation of heat in the combustion chamber (refer to Patent Literature 1). There are three kinds of forms of heat transmission (heat transfer) including heat conduction, convection, and radiation (heat emission) In the case of heat conduction, heat is transmitted by direct contact between objects without movements of the objects, and in the case of convection, heat is indirectly transmitted via a flow of a fluid, and by both of these, heat is transmitted as thermal vibrations. On the other hand, in the case of radiation, heat is transported when an object as a source of transportation emits electromagnetic waves and an object as a transportation destination absorbs the electromagnetic waves. In the case of radiation, no substance intervenes between the two objects, and heat is transmitted even in vacuum.

Heat transfer from a combustion chamber of an engine to a poppet valve is also caused in the three forms of heat conduction, convection, and radiation. In Patent Literature 1 described above, a recess is formed on a valve: head surface, and by filling this recess with a heat-resistant porous material, heat dissipation from the combustion chamber is suppressed. As this porous material, nonwoven fabric (Paragraph 0036) made of heat-resistant metal such as stainless steel is shown by way of example. However, although a normal heat insulating material can insulate heat transfer caused by heat conduction and convection among the three forms of heat transfer, the normal heat insulating material transmits radiation heat, and a temperature decrease accordingly caused inside the combustion chamber cannot be avoided. Patent Literature 1 contains no description on radiation, and includes no idea of insulation of radiation heat.

In Patent Literature 2, an inner wall of a combustion chamber of an engine is coated with a heat insulating material consisting of a heat insulating porous layer made of ceramics and a surface dense layer made of ceramics (Paragraph 0023). Reflection of radiation heat by the surface dense layer at the time of fuel combustion is disclosed (Paragraph 0024).

CITATION LIST Patent Literatures

Patent Literature 1: Japanese Published Unexamined Patent Application No. 2012-72748

Patent Literature 2: WO2013/080389 A1

Non-Patent Literatures

Non-Patent Literature 1: http://www.landinst.jp/info/faq/faq3.html

Non-Patent Literature 2: http://www.fintech.co.jp/etc-data/housharitsu.htm

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

According to examination by the inventors, it became clear that the rough-surfaced nonwoven fabric described in Patent Literature 1 hardly caused reflection of heat including radiation, and the ceramics described in Patent Literature 2 did not cause sufficient reflection of radiation heat contrary to the description in Patent Literature 2. For example, Non-Patent Literature 1 and Patent Literature 2 describe electromagnetic wave emissivities of metals and ceramics, etc., and the emissivity is defined as (emissivity=1−reflectance −transmissivity) Therefore, the lower the emissivity, the higher the reflectance, however, the emissivity of ceramics is so high as 0.4 to 0.95, and the reflectance thereof is accordingly very low, and it is found that the electromagnetic wave reflection efficiency is not sufficient. The emissivities of aluminum and copper are 0.05 to 0.09, and reflectances thereof are very high. Reflection by metal owes much to action of free electrons, and electromagnetic waves are reflected by collective oscillation of free electrons that the reflection effect is high, and the above-described reflection has directivity. However, metals such as aluminum and copper lack high-temperature tolerance, and are obviously unavailable for an engine in which a combustion gas temperature reaches 2000° C. to 2500° C.

In Patent Literature 2, an outermost layer portion on a combustion chamber side has a radiation heat reflection mechanism, so that a heatproof temperature required for the material is high and an applicable material is limited, and adhesion of combustion residue and generation of an oxidation layer occur, and accordingly, the reflection function deteriorates. Therefore, even if ceramics are applied to the valve head surface of the poppet valve described in Patent Literature 1, this does not lead to suppression of heat dissipation by reflection of radiation heat.

The present invention was made based on the above-described inventor's knowledge on the prior literatures, and an object thereof is to provide a poppet valve that can stably maintain high combustion efficiency for a long period of time by suppressing heat dissipation caused by radiation by reflecting radiation heat from a combustion chamber of the poppet valve toward the combustion chamber.

Solution Means

In order to attain the object, a poppet valve according to the present invention (Claim 1) is configured so that, in a poppet valve including a head portion formed, integrally with one end side Of a stem portion, on the head portion, a heat insulating portion that is positioned on a combustion chamber side and a metal layer that is positioned on a stem portion side and insulates radiation heat are formed.

(Operation) when the poppet valve configured as described above is used as an engine valve, heat of combustion flame produced by fuel combustion in the combustion chamber and a combustion gas generated by combustion is transmitted from the combustion chamber toward the poppet valve in the forms of heat conduction, convection, and radiation. In the heat of the combustion gas caused by heat conduction and convection is insulated by a heat insulating space on a combustion chamber side of the valve head of the head portion of a valve main body and a heat insulating region (heat insulating portion) obtained by filling the heat insulating space with a heat insulating material. Radiation heat being heat transported as electromagnetic waves passes through the heat insulating region and comes into contact with lustrous metal.

Heat caused by heat conduction and convection is insulated by the heat insulating portion and does not reach the metal, so that a temperature of the combustion gas that comes into contact with the metal greatly decreases, and even metal that lacks high-temperature tolerance can reflect radiation heat toward the combustion chamber without deterioration, and prevents the heat from being transmitted through the valve main body and dissipating, and makes the radiation heat stay inside the combustion chamber, and accordingly, heat of the combustion gas can be prevented from being cooled by the valve and combustion efficiency can be accordingly improved. In particular, although the metal is exposed to the heat of the combustion gas via the heat insulating portion, in other words, heat principally caused by radiation that cannot be insulated by the heat insulating portion, the heat of the combustion gas caused by heat conduction and convection is not directly transmitted to the metal, so that even a material whose heatproof temperature is low can be selected as the metal. By providing a radiation heat reflection mechanism inside the valve, the reflection performance can be prevented from being deteriorated by contamination such as adhesion of combustion residue and generation of an oxidation layer. The metal in the present invention includes a metal alloy as well.

A metal layer of the present invention needs to have radiation heat insulation performance. A metal with radiation heat insulation performance normally has a lustrous surface or a mirror surface, however, even if the metal does not have lustrous surface or a mirror surface, it can be used as the metal in the present invention as long as the metal has radiation heat insulation performance. In the case of a metal that does not have radiation heat insulation performance, after the metal is provided with radiation heat insulation performance by glazing or mirroring the surface thereof, the metal is allowed to be used as the metal in the present invention. In particular, when the temperature of the combustion gas produced inside the combustion chamber is 2500° C., a wavelength of emission of the heat of the combustion gas is 1.0 μm (wavelength at 1500° C. is 1.6 μm) based on Wien's displacement law, and the reflectance of the metal is high in this wavelength region, so that its radiation heat insulation performance is high. Therefore, metal usable in the present invention has radiation heat insulation performance much greater than that of ceramics or the like.

According to claim 2, in the poppet valve according to claim 1, a hollow portion extending along a head surface is formed in the head portion, a metal layer that insulates radiation heat is formed on a upper end surface of the hollow portion, and a heat insulating portion is formed between the metal layer and a bottom surface of the hollow portion.

(Operation) in the poppet valve configured as described above, the hollow portion is filled with a gas or a heat insulating material with low heat conductivity, or the hollow portion is kept in a vacuum. By properly selecting the conditions of the hollow portion, an optimum heat insulation effect is obtained.

According to claim 3, in the poppet valve according to Claim 1, a metal layer that insulates radiation heat is formed on a bottom surface of the head portion, and a heat-insulating surface treatment layer is formed on a combustion chamber side of the metal layer that insulates radiation heat.

(Operation) In the poppet valve configured as described above, a hollow portion is not formed, so that manufacturability of the valve can be improved.

According to claim 4, in the poppet valve according to claim 1, the metal is selected among aluminum, copper, and an aluminum alloy. Metals other than aluminum which constitute the aluminum alloy are copper, manganese, silicon, magnesium, zinc and nickel, etc.

(Operation) Aluminum and copper are preferable materials since they are comparatively light in weight and have high radiation heat reflection efficiency. An aluminum alloy also has radiation heat reflective power, and can improve fuel efficiency.

According to claim 5, in the poppet valve according to claim 1 or 2, the metal is foil-shaped or sheet-shaped. An aluminum foil and a copper foil normally have luster by themselves, and by directly attaching, etc., an aluminum foil or a copper foil to a combustion chamber side of the valve head via the heat insulating region, heat of radiation heat reflection can be prevented from scattering to the outside, and this contributes to improvement in fuel efficiency along with improvement in combustion efficiency. Similarly, in a case where the metal is molded into a sheet, by positioning and using the metal at a predetermined port ion, radiation heat can be reflected.

According to claim 6, in the poppet valve according to claim 1, the metal layer is a coating formed by surface treatment selected among physical vapor deposition (PVD), thermal spraying, and plating. The metal layer in the present invention may he an existing foil or sheet, or may be formed. by the surface treatment, and by such surface treatment, a metal layer with high radiation heat insulation performance can be obtained.

Effects of the Invention

With the poppet valve according to the present invention, by preventing heat generated in a combustion chamber from scattering to the outside by effectively insulating heat transfer in all of the forms of heat conduction, convection, and radiation of heat of a combustion flame and a combustion gas inside the combustion chamber, combustion efficiency loss due to cooling can be reduced. Even if the high-temperature tolerance of the metal forming the metal layer with high radiation heat insulation performance is not sufficient, heat caused by heat conduction and convection of the heat of the combustion gas is removed by the heat insulating portion, and only heat caused by radiation reaches the metal layer, so that metal deterioration hardly occurs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a poppet valve according to a first example of the present invention.

FIG. 2 is an enlarged sectional view taken along line A-A in FIG. 1.

FIG. 3 is a longitudinal sectional view of a poppet valve according to a second example of the present invention.

FIG 4 is a longitudinal sectional view of a poppet valve according to a third example of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment of the present invention is described based on examples.

FIG. 1 and FIG. 2 show a hollow poppet valve for an internal combustion according to a first example of the present invention.

In FIG. 1, the reference sign 10 denotes a poppet valve made of a heat-resistant alloy, including a valve head portion 14 formed integrally with one end side of valve stem portion 12 extending straight via a rounded fillet portion 13 whose outer diameter gradually increases, and on an outer circumference of the valve head portion 14, a tapered valve seat face 16 is provided. A shell 11 is configured by forming a head portion shell 14 a integrally with one end side of the stem portion 12.

On a upper end surface 14 b on a head surface 24 side of the valve head portion 14, a radiation heat reflection surface (metal layer that insulates radiation heat) 17 made of a foil-shaped or sheet-shaped metal on which, preferably, a mirror surface is formed, is formed by thermal spraying, etc., and joined, or a metal molded into a sheet is joined by a method such as welding. Usable metals include aluminum and copper, and further, an alloy of these metals, specifically, an alloy of aluminum.

Normally, a foil-shaped metal has a mirror surface and radiation heat: insulation performance, so that it can be used as it is, however, a sheet -shaped metal or a metal formed by surface treatment may not have sufficient radiation heat insulation performance. In this case, the surface of the metal needs to be subjected to treatment so as to have luster to improve the radiation heat insulation performance. An example of metal lustering treatment is metal surface polishing.

Next, a cap 18 is attached to the upper end surface 14 b of the valve head portion 14 on which the radiation heat reflection surface 17 is formed. This cap 18 has a discoid shape having an upward folded portion 18 a formed by folding the rim portion upward, and further, on an inner side upper surface, arc-shaped ribs 18 b obtained by dividing equally a donut-shaped circular ring into quarters, are formed by integral molding or welding. When the upward folded portion 18 a of the cap 18 is fixed by welding, etc., to the upper end surface 14 b of the valve head portion 14, the respective ribs 18 b support the upper end surface 14 b of the valve head portion 14 via the radiation heat reflection surface 17. Between an upper surface of the cap 18 and the upper end surface 14 b of the valve head portion 14, a hollow portion 1 is formed. By forming a vacuum in the inside of the formed space, heat conduction from the combustion chamber side is insulated, and the space functions as a heat insulating space. Even by filling this space with air or a gas such as argon, it serves as a heat insulating space. In the case of FIG. 1, the upper surface of the cap 18 serves as a bottom surface 25 of the hollow portion.

In FIG. 1, the reference sign 2 denotes a cylinder head, the reference sign 6 denotes an exhaust port extending from a combustion chamber 4, and on a rim portion of an opening of the exhaust port 6 leading to the combustion chamber 4, a toric valve seat insert 8 having a taper with which the valve seat face 16 of the valve 10 can come into contact is provided. The reference sign 3 denotes a valve insertion hole provided in the cylinder head 2, and the valve insertion hole 3 is configured by a cylindrical valve guide 3 a with which the stem portion 12 of the valve 10 comes into sliding contact. The reference sign 9 denotes a valve, spring that biases the valve 10 in a valve closing direction (upward in FIG. 1), and the reference sign 12 c denotes a cotter groove provided on an end portion of the valve stem portion 12. In the stem portion 12, a longitudinal hollow portion 21 is formed, and the hollow portion 21 makes the hollow portion (heat insulating portion) 19 and a lower surface of the stem end member 12 b communicate with each other.

The shell 11 and the cap 18 that are portions to be exposed to a high temperature gas of the combustion chamber 4 and the exhaust port 6 are made of heat-resistant steel, and on the other hand, the stem end member 12 b that is not required to be as heat-resistant as the shell 11 and the cap 18 while being required to have mechanical strength is made of general steel.

When a fuel burns in the combustion chamber 4 of the hollow poppet valve 10 configured as described above, heat of a high-temperature combustion gas is generated, and this heat of the combustion gas passes through the cap 18 of the poppet valve 10 and reaches the hollow portion (heat insulating portion) 19. Among heat conduction, convection, and radiation as heat transfer forms for the heat of the combustion gas, heat conduction and convection are insulated by this heat insulating portion 19, and the heat of the combustion gas is not transmitted from the radiation heat reflection surface 17 toward the valve head portion 14. Radiation heat in the heat of the combustion gas is reflected by the radiation heat reflection surface 17 made of aluminum, etc., and passes through the cap 18 and returns to the inside of the combustion chamber 4. Therefore, in the poppet valve 10 according to the present example, heat conduction, convection, and radiation as the heat transfer forms for the heat of the combustion gas are suppressed, and an amount of energy generated by combustion of the fuel to he drawn as heat to the outside via the valve main body is reduced (cooling loss is reduced).

In the present example, it became clear that as a material of the radiation heat reflection surface, aluminum, copper, or an aluminum alloy could be used, and unlike ceramics described in Patent Literature 2, it could reflect much of radiation heat and return it to the inside of the combustion chamber.

FIG. 3 shows a poppet valve for an internal combustion according to a second example of the present invention. A hollow poppet valve 10A according to the second example is a modification of the first example, and the same member as in the first example is designated by the same reference sign and description is omitted. In the second example, between a upper end surface 14 b′ and a bottom surface 25′ of a discoid cap 18′, a hollow portion 19′ being a spherical (domed) space is formed, and on an inner circumferential surface except for a lower end rim of the hollow portion 19′, a radiation heat reflection surface 17′ is formed by coating, and to a lower end of the hollow portion 19′, the discoid cap 18′ is fitted. A small-diameter hollow portion S is formed upward from a portion slightly above the radiation heat reflection surface 17′ in the stem portion 12 and the inside of this small-diameter hollow portion S is loaded with a coolant 23 (for example, metallic sodium whose melting point is approx. 98° C.) having higher heat conductivity than the base material of the engine valve, together with an inert gas. Inside this small-diameter hollow portion S, a stepped portion 22 is formed, and therefore, when the coolant 23 inside the small-diameter hollow portion S is moved in the up-down direction by inertia applied when the valve 10A opens or closes, a turbulence is generated near the stepped portion 22 and the coolant 23 is agitated, and accordingly, a heat dissipation effect (heat conductivity) at the valve stem portion 12 is improved. By insulating heat of the combustion gas on the combustion chamber side, the heat is not dissipated via the valve, and by the heat dissipation effect of the valve stem portion, the heatproof temperature required for the material can he lowered.

FIG. 4 shows a poppet valve for an internal combustion according to a third example of the present invention. The poppet valve 10B according to the third example is a modification of the first example, and the same member as in the first example is designated by the same reference sign and description is omitted. In the third example, a head portion 14B is molded integrally with a combustion chamber 4 side of a solid stem portion 12B, and in this example, no hollow portion is formed. On a bottom surface 15 of the head portion 14B of the valve 10B, a radiation heat reflection surface 17″ is formed so that both ends are not exposed, and on the surface of the radiation heat reflection surface 17″, a coating of a surface treatment heat insulating layer 18 with heat conductivity of 3 W/mK or less or a coating of a plate-shaped low heat-conductivity material with heat conductivity of 3 W/mK or less is formed. The formed surface treatment heat insulating layer 18 c has the same effect as the heat insulating space of the hollow portion 19 of the first example, and heat of a high-temperature combustion gas generated in the combustion chamber passes through the surface treatment heat insulating layer 18 c of the poppet valve 10B and reaches the radiation heat reflection surface 17″. Among heat conduction, convection, and radiation as heat transfer forms for the heat of the combustion gas, heat conduction and convection are insulated by the surface treatment heat insulating layer 18 c with low heat conductivity, and radiation is reflected to the inside of the combustion chamber 4 by the radiation heat reflection surface 17″. At this time, the radiation heat reflection surface 17″ is surrounded by the bottom surface 15 of the head portion 14B and the surface treatment heat insulating layer 18 c and is not exposed to the atmosphere, so that metal without heat resistance such as aluminum can also be used as a material of the radiation heat reflection surface 17″. Therefore, in the poppet valve 10B according to the present example, heat conduction, convection, and radiation as heat transfer forms for the heat of the combustion gas are suppressed, and an amount of energy generated by combustion of the fuel to be drawn as heat to the outside via the valve main body is reduced (cooling loss is reduced). The surface treatment heat insulating layer 18 c with low heat conductivity is formed by coating by means of atmospheric plasma spraying, etc.

REFERENCE SIGNS LIST

2: Cylinder head

3: Valve insertion hole

3 a: Valve guide

4: Combustion chamber

6: Exhaust port

8: Valve seat insert

9: Valve spring

10, 10A, 10B: Poppet valve

11, 11A: Shell

12: Stem portion

12 b: Stem end member

12 c: Cotter groove

13: Fillet portion

14, 14B: Head portion

14 a: Head portion shell

14 b: Upper end surface

15: Bottom surface

16: Valve seat face

17, 17, 17″: Radiation heat reflection surface (metal layer that insulates radiation heat)

18, 18′: Cap

18 a: Folded portion

18 b: Arc-shaped rib

18 c: Surface treatment heat insulating layer

19, 19′: Hollow portion (heat insulating portion, heat insulating space)

21: Hollow portion

22: Stepped portion

23: Coolant

24, 24′: Head surface

25, 25′: Bottom surface 

1. A poppet valve including a head portion formed integrally with one end side of a stem portion, wherein, on the head portion, a heat insulating portion that is positioned on a combustion chamber side and a metal layer that is positioned on a stem portion side and insulates radiation heat are formed.
 2. The poppet valve according to claim 1, wherein a hollow portion extending along a head surface is formed in the head portion, a metal layer that insulates radiation heat is formed on a upper end surface of the hollow portion, and a heat insulating portion is formed between the metal layer and a bottom surface of the hollow portion.
 3. The poppet valve according to claim 1, wherein a metal layer that insulates radiation heat is formed on a bottom surface of the head portion, and a heat-insulating surface treatment layer is formed on a combustion chamber side of the metal layer that insulates radiation heat.
 4. The poppet valve according to claim 1, wherein the metal is selected among aluminum, copper, and an aluminum alloy.
 5. The poppet valve according to claim 1, wherein the metal is foil-shaped or sheet shaped.
 6. The poppet valve according to claim 1, wherein the metal layer is a coating formed by surface treatment selected among physical vapor deposition (PVD), thermal spraying, and plating.
 7. The poppet valve according to claim 2, wherein the metal is selected among aluminum copper, and an aluminum alloy.
 8. The poppet valve according to claim 3, wherein the metal is selected among aluminum, copper, and an aluminum alloy.
 9. The poppet valve according to claim 2, wherein the metal is foil-shaped or sheet shaped.
 10. The poppet valve according to claim 3, wherein the metal is foil-shaped or sheet shaped.
 11. The poppet valve according to claim 4, wherein the metal is foil-shaped or sheet shaped.
 12. The poppet valve according to claim 2, wherein the metal layer is as coating formed by surface treatment selected among physical vapor deposition (PVD), thermal spraying, and plating. 